1. Field of the Invention
The present invention relates to an imaging apparatus equipped with an anti-shake (image shake correction/image stabilizing/shake reduction) system.
2. Description of the Related Art
In recent years, mobile electronic devices which are designed mainly for taking still/moving photographic images, such as digital cameras (still-video cameras) and digital camcorders (motion-video cameras), and other mobile electronic devices which are designed to be capable of taking such photographic images as a subsidiary function, such as mobile phones equipped with a camera and tablet computers, etc., equipped with a camera, have become widespread, and there has been a demand to miniaturize of the imaging units incorporated in these types of mobile electronic devices. In order to miniaturize an imaging unit, it is known to construct an optical system of an imaging unit out of a bending optical system which reflects (bends) light rays using a reflecting surface of a reflector such as a prism or a mirror. Using a bending optical system in an imaging unit makes it possible to achieve a reduction in thickness of the imaging unit, especially in the direction of travel of the incident light emanating from an object which is to be photographed.
In addition, there is a demand for imaging units to be equipped with a so-called anti-shake (image shake correction/image stabilizing/shake reduction) system that is designed to reduce image shake on an image plane that is caused by vibrations such as hand shake. The following four different types of imaging units are known in the art as imaging units using a bending optical system which are equipped with an anti-shake system: a first type (disclosed in Japanese Unexamined Patent Publication Nos. 2009-86319 and 2008-268700) in which an image sensor is moved in directions orthogonal to an image plane to reduce image shake, a second type (disclosed in Japanese Unexamined Patent Publication No. 2010-128384 and Japanese Patent No. 4,789,655) in which a lens disposed behind a reflector (on the image plane side) that has a reflecting surface is moved in directions orthogonal to an optical axis to reduce image shake, a third type (disclosed in Japanese Unexamined Patent Publication Nos. 2007-228005, 2010-204341, 2006-330439, and Japanese Patent No. 4,717,529) in which the angle of a reflector (a reflecting surface thereof) and the angle of a lens adjacent to the reflector are changed to reduce image shake, and a fourth type (disclosed in Japanese Unexamined Patent Publication Nos. 2006-166202 and 2006-259247) in which the entire imaging unit is tilted/inclined to reduce image shake.
An anti-shake system using voice coil motors (VCMs), which generate force (driving force) by application of a current (voltage) across the terminals of the coil positioned inside the magnetic field of a permanent magnet, for driving an optical element (anti-shake optical element) to reduce image shake is known in the art (disclosed in Japanese Unexamined Patent Publication Nos. 2009-86319, 2010-128384, 2007-228005, and Japanese Patent No. 4,789,655). Information on the position of the anti-shake optical element can be obtained with sensors (e.g., Hall sensors) that measure the change in the magnetic field.
The first type of anti-shake system tends to become complicated in structure and tends to increase in cost because a circuit board connected to the image sensor is moved in order to follow movements of the image sensor, which requires electrical components that are provided around the image sensor to also be movable components in addition to the image sensor. In addition, the periphery of the imaging surface of the image sensor is required to be dust tight; however, in small imaging units intended for being incorporated into a mobile phone or a tablet computer, etc., it is difficult to secure sufficient space for allowing the image sensor to perform an anti-shake (image shake correction/image-stabilizing/shake reduction) operation while maintaining the dust-tight structure of the image sensor.
The second type of anti-shake system has a structure such that the moving direction of the lens group, disposed behind the reflector, during an anti-shake operation corresponds to the direction of the thickness of the imaging unit (i.e., the forward/rearward direction of the imaging unit, wherein the direction toward an object to be photographed refers to the forward (front) direction of the imaging unit), and hence, there is a problem with providing enough space to house such an anti-shake structure in a slimmed-down imaging unit. In other words, the slimming-down of the imaging unit is limited if this type of anti-shake system is used. There is a similar problem also in the type of anti-shake system in which an image sensor is moved, instead of a lens group, in the direction of the thickness of the imaging unit.
The third type of anti-shake system requires a large space for allowing the reflector and the lens group to tilt/incline, and accordingly, the imaging unit is easily enlarged in size. The fourth type of anti-shake system requires a larger space for allowing the entire imaging unit to be tilted/inclined to reduce image shake.
Accordingly, there has been a demand for an anti-shake system that utilizes a different manner of driving an anti-shake optical element from those of the above described types of imaging units and that is advantageous for miniaturization and slimming-down of the imaging apparatus. In addition, in the case where voice coil motors (VCMs) are used as drive sources of an anti-shake system, arranging elements thereof such as permanent magnets, coils and sensors in a space-efficient manner in addition to an anti-shake driving manner is also important for achieving miniaturization of the imaging apparatus.
Voice coil motors (voice coil linear motors) that provide linear motion can transmit power with no need for a mechanism to convert rotational motion into linear motion, and therefore, if voice coil motors are used in an anti-shake system as drive sources which move an anti-shake optical element in a plane orthogonal to an optical axis, the anti-shake system can be easily simplified in structure. On the other hand, permanent magnets and coils which constitute voice coil motors are typically flat in shape, each having a wide surface along a plane (orthogonal to an optical axis of the anti-shake optical element) in which the anti-shake optical element moves, so that the installation space for the permanent magnets and the coils in this plane tends to be large. In the voice coil motors for use in an anti-shake system in particular, a combination of a permanent magnet and a coil and another combination of a permanent magnet and a coil, these combinations being orthogonal in linear moving direction to each other, are used and arranged around the anti-shake optical element, and accordingly, it is necessary to pay attention to the arrangement of the voice coil motors and associated sensors when it is attempted to miniaturize and reduce the thickness of an imaging unit equipped with an anti-shake system using voice coil motors as drive sources for driving an anti-shake optical element.
Additionally, in the case where voice coil motors in which permanent magnets are mounted on a movable member, i.e., so-called moving-magnet type voice coil motors, are used for an anti-shake system, there is a possibility of magnetic materials around the voice coil motors exerting an influence on the magnetic fields of the permanent magnets and thereby deteriorating the driving accuracy of the anti-shake system, so that countermeasures against this problem are required.